My Audi 80 sport has developed a noise. The noise is a low pitch vibratory pulse which occurs under acceleration between 2500 and 3000 rpm. The noise also increases in frequency through this rpm range. The noise is not present when the car is out of gear and then throttle applied to the relevant rpm, and also does not occur when the car is first started (it takes till at lease 60 degrees c on the temp gauge to occur). I am toying with the idea that it's a gearbox problem but the noise sounds suspiciously like a bearing.